Advanced wireless devices may have multiple radios that operate on the same, adjacent, or harmonic frequencies. The radios may provide access to networks such as wireless wide area network (WWAN), a wireless local area network (WLAN), a wireless personal area network (WPAN), Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), BeiDou navigation satellite system, etc. Some combinations of radios can cause co-existence issues due to interference between the respective frequencies. In particular, when one radio is actively transmitting at or close to the same frequency and at a same time that another radio is receiving, the transmitting radio can cause interference to (i.e., de-sense) the receiving radio. For example, same-band interference may occur between Bluetooth (WPAN) and 2.4 GHz WiFi (WLAN); adjacent band interference between WLAN and Long Term Evolution (LTE) band 7, 40, 41; harmonic interference may occur between 5.7 GHz ISM and 1.9 GHz Personal Communications Service (PCS); and an intermodulation issue may occur between 7xx MHz and a GPS receiver.
Analog interference cancellation (AIC) cancels interference between a transmitter radio and a receiver radio by matching gain and phase of a wireless coupling path signal and in a wired AIC path, as shown in FIG. 1, where dt is a transmitted signal from a transmitter (aggressor) radio 102, and hc is a coupling channel (wireless coupling path signal) from the transmitter radio 102 to a receiver (victim) radio 104. AIC 106 attempts to cancel the impact of the coupling channel hc as reflected via the negative sign on the output of AIC 106. The cancellation may be applicable not only for the separate transmitter-receiver antenna scenarios, but also for the scenarios where the transmitter(s) and receiver(s) share the same antenna(s). In the latter case, over-the-air coupling channel may be further simplified to wired channel.
Analog interference cancellation may be performed utilizing adaptive filter coefficients computed either at RF or at baseband, where baseband means utilizing a digital implementation, for example, a field programmable gate array (FPGA), digital signal processing (DSP) elements or application-specific integrated circuits (ASIC). Baseband coefficient computation may allow more precise coefficient determination which may lead to optimal interference cancellation. The coefficients thus computed are sent to the analog interference cancellation (AIC) circuit for conditioning the reference signal to cancel the undesired interference. However, one disadvantage of baseband processing is undesired DC offset leakage. That is, the reference signal, after AIC conditioning, may have a residual dc bias which may degrade the interference cancellation.